1. Field of the Invention
The present invention relates to a band control system for a digital subscriber network and a band control method therefor. More particularly, the present invention relates to a band control system implementing flexible control and efficient use of a band between IADs (Integrated Access Devices) and a DSLAM (Digital Subscriber Line Access Multiplexer) situated at subscriber stations and a center, respectively, and a control method therefor.
2. Description of the Background Art
A VoDSL (Voice over Digital subscriber Line) network using an ATM (Asynchronous Transfer Mode) communication system and a DSL technology provides a transfer path for multimedia communication using voice, data and image. DSL technologies implement high-speed digital transfer over metallic cables, i.e., existing telephone subscriber lines.
A problem with the conventional DSL technologies is that the transfer rate is dependent on the quality of metallic cables and transfer distance and therefore indefinite despite a preselected transfer rate. Consequently, a communication band statistically set beforehand brings about the congestion of ATM cells and thereby causes some users to be blocked. It is therefore necessary to dynamically control band assignment in order to obviate the congestion of ATM cells.
Japanese Patent Laid-open Publication No. 2000-184061, for example, discloses a technology for dynamically controlling band assignment in a DSL communication system. It has been customary with conventional technologies, including the above technology, to send band control information indicative of the variation of a communication band by using special ATM cells, e.g., RM (Resource Management) cells. This, however, presses the communication band and thereby makes the use of the frequency band uneconomical when such special ATM cells are used to dynamically guarantee the band during communication.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No-11-331192.